Scalable cross-point resistive switching memory and mechanism through an understanding of H₂O₂/glucose sensing using an IrO_x/Al₂O₃/W structure

The resistive switching characteristics of a scalable IrO_x/Al₂O₃/W cross-point structure and its mechanism for pH/H₂O₂ sensing along with glucose detection have been investigated for the first time. Porous IrO_x and Ir³⁺/Ir⁴⁺ oxidation states are observed via high-resolution transmission electron microscope, field-emission scanning electron spectroscopy, and X-ray photo-electron spectroscopy. The 20 nm-thick IrO_x devices in sidewall contact show consecutive long dc cycles at a low current compliance (CC) of 10 μA, multi-level operation with CC varying from 10 μA to 100 μA, and long program/erase endurance of >10⁹ cycles with 100 ns pulse width. IrO_x with a thickness of 2 nm in the IrO_x/Al₂O₃/SiO₂/p-Si structure has shown super-Nernstian pH sensitivity of 115 mV per pH, and detection of H₂O₂ over the range of 1-100 nM is also achieved owing to the porous and reduction-oxidation (redox) characteristics of the IrO_x membrane, whereas a pure Al₂O₃/SiO₂ membrane does not show H₂O₂ sensing. A simulation based on Schottky, hopping, and Fowler-Nordheim tunneling conduction, and a redox reaction, is proposed. The experimental I-V curve matches very well with simulation. The resistive switching mechanism is owing to O^2- ion migration, and the redox reaction of Ir³⁺/Ir⁴⁺ at the IrO_x/Al₂O₃ interface through H₂O₂ sensing as well as Schottky barrier height modulation is responsible. Glucose at a low concentration of 10 pM is detected using a completely new process in the IrO_x/Al₂O₃/W cross-point structure. Therefore, this cross-point memory shows a method for low cost, scalable, memory with low current, multi-level operation, which will be useful for future highly dense three-dimensional (3D) memory and as a bio-sensor for the future diagnosis of human diseases.